OT - Sizing a water well submersible pump

I'm trying to determine what size pump to buy.

Below is a typical submersible water well pump chart that shows HP vs head and flow.

For my shop's well, I have a Red Jacket 1.5HP pump. My well depth is 66 feet. The well service guys I've talked to both tell me it's way oversized and said a 1HP is more than enough. The chart seems to echo this....the 1.5HP pump does not even begin to chart until a 120 foot depth.

But, I told one of the well guys I couldn't maintain very good water pressure if too many loads were on it at the same time - especially the outdoor sprinkler system. He said, "Oh well, in that case you should stick with a 1.5HP..."

The other guy told me if you oversized the pump, it would fail sooner as the thrust bearings did not have enough load on them. This sounds a little fishy but not 100% fishy.

Most of all, they both told me the average years of service you can expect out of a pump is 7. My pump is almost 23 years old and working perfectly. So the early bearing failure theory doesn't seem to hold much water, lol.

Anyone have any further insights? I have no concern over the added price or added electricity use of the larger pump....I just want what's 'best' but still not sure what that is.

Its been ok for 23 years, why worry about it now? The only thing wrong , its wasted electricity, If you dont need the flow rate the motor will drop amps and the water will heat up a little, and the water pressure will increase...If you need the flow, pressure will drop amps goes up and more gpm pumped...stick with the big pump ( the pump guys sucks if he thinks it will kick out the bearing)...Phil

Put a larger accumulator tank on it then go not matter as much.

It will fill tank and rest.

Constant running for high loads like sprinklers can be issue if the pump cannot cycle.

Sprinkler patterns vary with pressure if cycling.

Pump guys want to sell their service, seek help from commercial irrigation guys as they do this from other side.

Meaning control and design of system to work with whatever source.

Sent from my SAMSUNG-SM-G930A using Tapatalk

There is more to this than the well depth. You need to know how much pump down the well water level will drop while running. This will give you the distance from ground level to water level. This answer is the real pump head in distance for the well portion of the calculation. You must also add the desired operating pressure converted to head to the well head number.

Example: If you want a 50psi operating pressure, divide the 50psi by .433 to convert to head which equals 115ft.

If your well is 66ft and assume for example that the water table is at 40 ft., then that means your application has 155ft of head.

So now you can use the chart to see what the 1.5hp pump will deliver at 155ft. If you reduce the pressure to 30psi, your total head will be 109.28 ft. This makes that 1.5hp pump not as oversized as you might think.

I am not an expert but do have a 61 foot well and have replaced components. You are not looking at the entire system. You need to consider factors other than just the pump like:

1. How big is your pressure tank?
2. Is it a modern style tank with a bladder? If so is the bladder still good?
3. What is the rating of your pressure regulator? 20 psi/40psi or 30psi/50psi ?
4. What is the size of your well pipe from the pump to the tank? 1" or 1.25" ?
5. How is the main feed piping inside your shop sized before things split off to hot/cold? 1" or 3/4" ?
6. What is the maximum flow you can draw from your well before you run it dry?

After you consider all these factors you can figure out why you can not maintain the pressure you want. My guess is that 1HP is plenty but you have some other issue in your system that can be improved.

When you consider how all these options interact

Have you considered a VFD pump? That seems to be what is the coming thing around here. Pump only the amount of water you need.

GregSY said:

I'm trying to determine what size pump to buy.

Below is a typical submersible water well pump chart that shows HP vs head and flow.

For my shop's well, I have a Red Jacket 1.5HP pump. My well depth is 66 feet. The well service guys I've talked to both tell me it's way oversized and said a 1HP is more than enough. The chart seems to echo this....the 1.5HP pump does not even begin to chart until a 120 foot depth.

But, I told one of the well guys I couldn't maintain very good water pressure if too many loads were on it at the same time - especially the outdoor sprinkler system. He said, "Oh well, in that case you should stick with a 1.5HP..."

The other guy told me if you oversized the pump, it would fail sooner as the thrust bearings did not have enough load on them. This sounds a little fishy but not 100% fishy.

Most of all, they both told me the average years of service you can expect out of a pump is 7. My pump is almost 23 years old and working perfectly. So the early bearing failure theory doesn't seem to hold much water, lol.

Anyone have any further insights? I have no concern over the added price or added electricity use of the larger pump....I just want what's 'best' but still not sure what that is.





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After 23 years? It seems as if at least the formation you've tapped as source has the flow and recovery rate to support the pump you have.

Manifold in a second accumulator - or make the new one larger - and you should be able to keep on using the same goods.

I had 330-odd feet, steel cased, cemented into rock, drilled through to tap a sand below the formation.

Got me SAFE water, if a tad acidic, Fairfax County, Va, But the pumps were only good for 2 years plain-jane, 5 to 7 years as we upgraded to "premium", all stainless. Pulling that depth to swap one out was a nuisance, too!

Why change what has worked so much better for yah than average? Those "well experts" should be asking YOU for advice. Not you asking THEM!

Did the service guys from the pump place have fishing tackle in their noses and lips...I'd look for someone more knowledgeable...certainly not on PM.

Stuart

I've got a 250ft water well. You should size your pump to be the "right" size to operate for extended periods, this is how you get good life on your pump. If you oversize it, it will fire on/off too often and will wear out faster. Pumps like to turn on and stay on. AND, you need a pressure tank or two which also helps even out the pump operation. Finally, you'll want to analyze your flow requirements and the HP to match your pressure requirements. You should reasonably expect 10-18 years of life on the pump depending on the original quality and the matchup as discussed here.

drcoelho said:

I've got a 250ft water well. You should size your pump to be the "right" size to operate for extended periods, this is how you get good life on your pump. If you oversize it, it will fire on/off too often and will wear out faster.

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Not only the pump.

One of our early failures was due to the "snubber" not doing its job. The gadget that (was SUPPOSED TO..) control the starting torque reaction "kick" from the pump so it didn't destroy the plastic waterline tubing by constant twisting, cycle after cycle.

First thing I do when getting a well call is get a copy of the well log if it is available. I can get it on line here in Ohio or from the local health department. Knowing what strata you go through, how much casing, static level, recovery rate, how far down the pump is set, is there a screen needed which is typical of fully cased wells. If your well log isn’t available you may look up your neighbors to get a general idea of what is going on in the area. Not always accurate as I’ve seen wells with low recovery at 2gpm and the neighbors with 15gpm and a few more doors down at 30gpm. Just a little more to think about.

Thanks all.

Just some further information....the pipe is 1-1/4", the tank is a 2 year old Gen-X-Trol 81 gallon bladder type. The water level in the well? I don't know. This area is not know for people running out of water so I assume from that it is a fairly healthy reservoir but...that could be a 65 foot deep water 4" diameter or 1 foot of water 5000 feet diameter.

I'm thinking I'll stay with 1.5HP. As for VFD pumps....no way on Earth will I add that level of complexity. Plus, one of the well guys told me the control alone is $1500 for that type of pump.

I've been quoted right around $2700 to do this job, and that's with the caveat that there could be added expenses (pipe, wiring, etc.) that go beyond the normal scope. Doing it myself, I should be able to save at least $1000 or a bit more.

It sounds like your previous pump was properly sized, 23 years says a lot. If the water quality is good, meaning that it doesn't destroy the pump in just a few years, 20 to 30 years on a properly sized pump is not uncommon.

Your well people sound a little off by stating the the thrust bearings wouldn't have a big enough load on them. I think he must be confused with the newer VFD driven domestic well pumps that are the latest fashion. There is a minimum RPM requirement by all MFG's that usually state that the pump minimum RPM be no less than 50% to maintain proper lubrication of the bearings. Since you are sticking with a Non-VFD system, that problem is of no concern.

One design criteria to be met is to keep the pump motor from overheating by requiring a minimum flow of water over the motor. Franklin motor, which makes just about all the submersible pump motors sold here in the States require the following:

4-inch Super Stainless = No minimum, but must have some water movement
4-inch High Thrust = ¼ ft/s
6-inch Motors = ½ ft/s
8-inch Motors = ½ ft/s

In a pump motor of your size a 2 foot minimum submergence is required.

Example:
For 3 to 10hp motors
A 4 inch pump in a 4 inch well casing requires a minimum of 1.2 GPM.
A 4 inch pump in 6 inch well casing requires a minimum flow of 13 GPM.
You can sleeve a pump motor to lower the minimum GPM's required for larger size casing to meet the ¼ ft/s or ½ ft/s if needed.

From the life that you got from your existing pump it's apparent you have meet all the above requirements!

The thing that is confusing is the chart you posted. It is small and I may have looked up the wrong one, but it appears that it is for a 5GS Model pump. Since you stated you are using it to supply a sprinkler system along with the shop, it doesn't make sense. The 5GS Models are rated at 5 GPM. With a 1-1/2hp pump, I would think a 25GS would be more appropriate and give you 5 times the water volume at the pressure you require and last just as long.

Afternoon,

To play it safe, stick with what the original scheme design called for.

However the new wet ends are a lot more efficient than 23 years ago, so you can downgrade the motor to 1 hp and still keep the same output your system was designed for by changing the wet ends. I used to run a 3hp motor to produce 5.4m3/hr and now am running a 2hp motor producing the same on one bore hole and 3 hp producing 9m3/hr where I was running a 5 HP previously. Total head we are on 70m (210 ft)

If the down pipe is 1.25" HDPE all you need is a couple of fellas to pull it up, change the HDPE coupling to the motor, and a cable jointing kit. You might want to change the safety rope and electric cable if been down that long.

Our motors don't last that long due to lightening strikes, single phasing and over voltage from the electric company. I have switched all pumps and motors to DAB brand.

tmt said:

I would think a 25GS would be more appropriate and give you 5 times the water volume at the pressure you require and last just as long.

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This is where having your well log or what the actual well recovery rate info comes into play. Too many times pumps that produce more water than the recovery rate of the well cause issues that may not show up for years if not right from the start.

Looking for flow restrictors or valves and screens between the pump and your expansion tank typically shed light on recovery issues. These are things often overlooked as “ oh that’s nice there’s a shut off valve and a sediment screen.” Its there for a reason.
Just trying to point out some of the not so obvious issues.
Regards Z

Drop an ice cube down the well and count the time to the splash to get water level. Or lower a weight on a string to get better accuracy but you risk hanging up on stuff downhole.
Bill D

The water pump in my well is 1.5 hp. It's used only for household in a rural area. The well contractor told me the following: The water table is around 90 feet and the pump is down at 140 feet with the well somewhat deeper. I was told something like 175 feet.

The tank is about 6' tall with something like 3' in diameter. (not sure of capacity.) The high pressure is set to shut off at 50 psi and the low will restart the pump at 25 psi.

The well was put down when the house was built new in 1976. We moved there in 1977 and there have been only a few problems and all of them on top of the ground. Once the pump quit and I called in a well shop and had the pump tested electrically and it was OK. The capacitors were weak and were replaced. - all OK after that.

Now and then, every couple of years or so, the well will stop working and it's always been an earwig in the points of the pressure switch. I can't seem to keep the little buggers out. LOL Takes about 5 minutes to shut off the breaker and blow out and file the points and then it starts up again.

If there's any question about HP, I'd go with a 1.5 hp. Just get the best quality pump you can and go with it.

Happy Trails!

Thanks again everyone.

I used to have a 30/50PSI switch, but about 5 years ago I went to a 40/60.....when the pressure would approach 30PSI there just wasn't enough water pressure and that was visible on sprinklers and when I would be using a garden hose to wash something off.

Sorry the chart is so poor, I'll try to upload a bigger version.

I was 'recommended' a Goulds pump as being high quality as it appears Red Jacket was bought out by someone and no longer exists. Another well service place said they use 'Weelo' (?) pumps but I couldn't even find reference to those.

The system seems to work properly in terms of pump run time. When it turns on, it runs for what seems a 'good' amount of time in order to recharge the tank.....in other words, it doesn't take 15 minutes nor does it take 15 seconds.

I was down in the basement to change my water filter and took a look a the box for my pump to see what I put in years ago. It is a 1/2 hp unit. As said previously my well is 61 ft deep. I use a 30-50 pressure switch. A 1/2 hp pump has worked fine for me for many years. Goulds is the gold standard for pump brands and I have used them before. They are only sold through dealers not in big box stores so are very pricey. I find the cheap pumps at Lowes work about as long. Since pumps are easy to change in a shallow ( less than 150 ft) well as 2 guys can pull it out in 5 minutes so if a cheap one lasts almost as long but costs half as much that is the way to go.

So the latest in my well pump saga is.....I pulled the pump out of the casing by about 12", enough to make some measurements. It turns out the person I bought the place from was wrong...the well is not 66 feet deep, but rather 225' deep. The top of the water sits 125' from the ground level.

So...my plan to use galvanized pipe is on shaky ground. 220 feet of galv. pipe will weight over 500lbs. and I get kinda freaky about hanging that much in the ground, all supported by a 4" PVC pipe casing.

I also learned the existing pump drop is 1-1/4" Sch 40 PVC pipe. This has worked well enough, but since I first started this thread we had a the Big Freeze here...the neighbor (who made no freeze preparations) had his wellhead freeze enough that when the pump kicked on, the PVC shattered and the entire pipe/pump fell down in the well. He had a well pump company come out and they were able to extract some lengths of the PVC but eventually told him they couldn't get it all out. It didn't help that since he put in the well, he added on two new buildings and there was no way to access the wellhead with a pole truck. Either way, he spent $18K getting a new well drilled.

So I'm not gonna go back with PVC.

The well supply providers (online) tell me people use poly pipe nowadays. This is the black plastic pipe sold in coils, SIDR dimensioned, 4710 material. I can buy this online though the shipping is high....but no one in Houston sells it. The ID is 1.25" which is smaller than the 1.38 ID of 1-1/4" galv pipe. But, the charts say it has a significantly lower coefficient of friction than galv pipe which helps. The poly pipe is much light, too - about 20% of the weight of galv pipe. I found one well place online that says they don't recommend poly pipe for depth over 100'...though they don't say why.

My question is.....has anyone used poly pipe and what were the results?